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PHY238Y Lecture 10

PHY238Y Lecture 10. The human ear (outer and middle) Physics of hearing (II) References: Haliday, Resnick, Walker: Fundamentals of Physics, 6 th ed. 2003, Ch. 18 (18.5, 18.6) Hallett et al.: Physics for the life sciences, 4 th ed., Ch.2 (2.6)

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PHY238Y Lecture 10

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  1. PHY238YLecture 10 • The human ear (outer and middle) • Physics of hearing (II) References: Haliday, Resnick, Walker: Fundamentals of Physics, 6th ed. 2003, Ch. 18 (18.5, 18.6) Hallett et al.: Physics for the life sciences, 4th ed., Ch.2 (2.6) K. Bogdanov: Biology in Physics: is Life Matter, Acad. Press 2000, Ch. 6 Hyper Physics: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html#c1 Thanks to dr. Rod Nave for the permission to use the above resource

  2. PHY238YLecture 10 • Structure of the human ear

  3. PHY238YLecture 10 • The outer ear, or pinna acts like a funnel to collect sound; • For a given sound intensity, a larger ear captures more of the sound wave and its energy; • The outer ear structures enhance the sensitivity of hearing.

  4. PHY238YLecture 10 • The outer ear • Sound perception: The Fletcher- Munson curves • The hearing curves show a significant minimum in the range 2000-5000 Hz with a peak sensitivity around 3500- 4000 Hz. • There is another enhanced sensitivity region at about 13,500 Hz. • The high sensitivity region at 2-5kHz is very important for the understanding of speech.

  5. PHY238YLecture 10 • The outer ear • The maximum sensitivity regions of human hearing can be modeled as closed tube resonances of the auditory canal. The observed peak at about 3700 Hz at body temperature corresponds to a tube length of 2.4 cm. The higher frequency sensitivity peak is at about 13 kHz which is somewhat above the calculated 3rd harmonic of a closed cylinder.

  6. PHY238YLecture 10 • Fletcher- Munson (equal loudness) curves

  7. PHY238YLecture 10 • The middle ear • The tympanic membrane or eardrum receives vibrations traveling up the auditory canal and transfers them through the tiny ossicles to the oval window, the port into the inner ear. The eardrum is ~ fifteen times larger than the oval window, giving an amplification of about fifteen compared to the oval window alone.

  8. PHY238YLecture 10 • The middle ear: ossicles • The three tiniest bones in the body couple the vibration of the eardrum and the forces exerted on the oval window of the inner ear • The ossicles form a compound lever which achieves a multiplication of force.

  9. PHY238YLecture 10 • The middle ear: Ossicle vibration • Ossicles achieve an amplification by lever action. The lever is adjustable under muscle action and may actually attenuate loud sounds for protection of the ear.

  10. PHY238YLecture 10 ODE TO THE OSSICLES (by Allison and Susan Sekuler) Every creature, live or fossicles, Cannot hear without their ossicles. Except, as hard as they may wish, There are no ossicles in fish. You might think this quite unfair, but fish do not live in air, so they simply do not care….

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